This application claims the priority of German patent document 100 16 185.5, filed Mar. 31, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a fuel cell system having an air supply for providing fuel to a fuel cell unit, and to a method of operating such a fuel cell system.
In methanol-fuelled fuel cell driven vehicles in particular, cold starting of the system requires a relatively large amount of energy, which generally must be provided by the vehicle battery. In the cold-start phase, a large electrical output is required particularly by the electricity supply of the gas generation system for providing the hydrogen gas for the fuel cell. A fuel cell system of this type is disclosed, for example, in German patent document DE-C2 43 22 767.
It is an object of the invention to provide a fuel cell system and a method of operating it, which reduces energy consumption in the event of a cold start.
This and other objects and advantages are achieved by the fuel cell system and method according to the invention in which a compressor having a variable internal compression ratio is used to supply the cathode side of a fuel cell with air. This arrangement allows compressor operation to be tailored to the different requirements during cold start and normal operation, so that energy consumption is improved and annoying noise emissions can be avoided.